Method of manufacturing a semiconductor on insulator structure by a pressurized bond treatment

ABSTRACT

A method is provided for preparing a semiconductor-on-insulator structure comprising a step of high pressure bonding.

CROSS REFERENCE TO RELATED APPLICATION(S)

This application claims the benefit of priority to U.S. provisionalapplication Ser. No. 62/304,389, which was filed 7 Mar. 2016, thedisclosure of which is hereby incorporated by reference as if set forthin its entirety.

FIELD OF THE INVENTION

The present invention generally relates to the field of semiconductorwafer manufacture. More specifically, the present invention relates to amethod of a semiconductor-on-insulator (e.g., silicon-on-insulator)structure.

BACKGROUND OF THE INVENTION

Semiconductor wafers are generally prepared from a single crystal ingot(e.g., a silicon ingot) which is trimmed and ground to have one or moreflats or notches for proper orientation of the wafer in subsequentprocedures. The ingot is then sliced into individual wafers. Whilereference will be made herein to semiconductor wafers constructed fromsilicon, other materials may be used to prepare semiconductor wafers,such as germanium, silicon carbide, silicon germanium, gallium arsenide,and other alloys of Group III and Group V elements, such as galliumnitride or indium phosphide, or alloys of Group II and Group VIelements, such as cadmium sulfide or zinc oxide.

Semiconductor wafers (e.g., silicon wafers) may be utilized in thepreparation of composite layer structures. A composite layer structure(e.g., a semiconductor-on-insulator, and more specifically, asilicon-on-insulator (SOI) structure) generally comprises a handle waferor layer, a device layer, and an insulating (i.e., dielectric) film(typically an oxide layer) between the handle layer and the devicelayer. Generally, the device layer is between 0.01 and 20 micrometersthick, such as between 0.05 and 20 micrometers thick. Thick film devicelayers may have a device layer thickness between about 1.5 micrometersand about 20 micrometers. Thin film device layers may have a thicknessbetween about 0.01 micrometer and about 0.20 micrometer. In general,composite layer structures, such as silicon-on-insulator (SOI),silicon-on-sapphire (SOS), and silicon-on-quartz, are produced byplacing two wafers in intimate contact, thereby initiating bonding byvan der Waal's forces, followed by a thermal treatment to strengthen thebond. The anneal may convert the terminal silanol groups to siloxanebonds between the two interfaces, thereby strengthening the bond.

After thermal anneal, the bonded structure undergoes further processingto remove a substantial portion of the donor wafer to achieve layertransfer. For example, wafer thinning techniques, e.g., etching orgrinding, may be used, often referred to as back etch SOI (i.e., BESOI),wherein a silicon wafer is bound to the handle wafer and then slowlyetched away until only a thin layer of silicon on the handle waferremains. See, e.g., U.S. Pat. No. 5,189,500, the disclosure of which isincorporated herein by reference as if set forth in its entirety. Thismethod is time-consuming and costly, wastes one of the substrates andgenerally does not have suitable thickness uniformity for layers thinnerthan a few microns.

Another common method of achieving layer transfer utilizes a hydrogenimplant followed by thermally induced layer splitting. Particles (atomsor ionized atoms, e.g., hydrogen atoms or a combination of hydrogen andhelium atoms) are implanted at a specified depth beneath the frontsurface of the donor wafer. The implanted particles form a cleave planein the donor wafer at the specified depth at which they were implanted.The surface of the donor wafer is cleaned to remove organic compounds orother contaminants, such as boron compounds, deposited on the waferduring the implantation process.

The front surface of the donor wafer is then bonded to a handle wafer toform a bonded wafer through a hydrophilic bonding process. Prior tobonding, the donor wafer and/or handle wafer are activated by exposingthe surfaces of the wafers to plasma containing, for example, oxygen ornitrogen. Exposure to the plasma modifies the structure of the surfacesin a process often referred to as surface activation, which activationprocess renders the surfaces of one or both of the donor water andhandle wafer hydrophilic. The surfaces of the wafers can be additionallychemically activated by a wet treatment, such as an SC1 clean orhydrofluoric acid. The wet treatment and the plasma activation may occurin either order, or the wafers may be subjected to only one treatment.The wafers are then pressed together, and a bond is formed therebetween. This bond is relatively weak, due to van der Waal's forces, andmust be strengthened before further processing can occur.

In some processes, the hydrophilic bond between the donor wafer andhandle wafer (i.e., a bonded wafer) is strengthened by heating orannealing the bonded wafer pair. In some processes, wafer bonding mayoccur at low temperatures, such as between approximately 300° C. and500° C. In some processes, wafer bonding may occur at high temperatures,such as between approximately 800° C. and 1100° C. The elevatedtemperatures cause the formation of covalent bonds between the adjoiningsurfaces of the donor wafer and the handle wafer, thus solidifying thebond between the donor wafer and the handle wafer. Concurrently with theheating or annealing of the bonded wafer, the particles earlierimplanted in the donor wafer weaken the cleave plane.

A portion of the donor wafer is then separated (i.e., cleaved) along thecleave plane from the bonded wafer to form the SOI wafer. Cleaving maybe carried out by placing the bonded wafer in a fixture in whichmechanical force is applied perpendicular to the opposing sides of thebonded wafer in order to pull a portion of the donor wafer apart fromthe bonded wafer. According to some methods, suction cups are utilizedto apply the mechanical force. The separation of the portion of thedonor wafer is initiated by applying a mechanical wedge at the edge ofthe bonded wafer at the cleave plane in order to initiate propagation ofa crack along the cleave plane. The mechanical force applied by thesuction cups then pulls the portion of the donor wafer from the bondedwafer, thus forming an SOI wafer.

According to other methods, the bonded pair may instead be subjected toan elevated temperature over a period of time to separate the portion ofthe donor wafer from the bonded wafer. Exposure to the elevatedtemperature causes initiation and propagation of cracks along the cleaveplane, thus separating a portion of the donor wafer. The crack forms dueto the formation of voids from the implanted ions, which grow by Ostwaldripening. The voids are filled with hydrogen and helium. The voidsbecome platelets. The pressurized gases in the platelets propagatemicro-cavities and micro-cracks, which weaken the silicon on the implantplane. If the anneal is stopped at the proper time, the weakened bondedwafer may be cleaved by a mechanical process. However, if the thermaltreatment is continued for a longer duration and/or at a highertemperature, the micro-crack propagation reaches the level where allcracks merge along the cleave plane, thus separating a portion of thedonor wafer. This method allows for better uniformity of the transferredlayer and allows recycle of the donor wafer, but typically requiresheating the implanted and bonded pair to temperatures approaching 500°C.

Complications associated with multilayer SOI structures includevariations in flatness and sensitivity to defects at the bond interface.Common solutions to this include CMP, which is costly and may leavescratches or thickness variation. The traditional SOI structurespecifications include electrical characteristic that can be easilyintegrated into devices.

SUMMARY OF THE INVENTION

The present invention is directed to a method for preparing a multilayersemiconductor on insulator structure that resists impurities containedin a handle substrate from having an influence on the device.

The present invention is further directed to a method of preparing amultilayer structure, the method comprising: bonding a donor dielectriclayer on a front surface of a single crystal semiconductor donorsubstrate to a front surface of a single crystal semiconductor handlesubstrate to thereby form a bonded structure, wherein (i) the singlecrystal semiconductor handle substrate comprises two major, generallyparallel surfaces, one of which is the front surface of the singlecrystal semiconductor handle substrate and the other of which is a backsurface of the single crystal semiconductor handle substrate, acircumferential edge joining the front surface and the back surface ofthe single crystal semiconductor handle substrate, a central planebetween the front surface and the back surface of the single crystalsemiconductor handle substrate, and a bulk region between the front andback surfaces of the single crystal semiconductor handle substrate and(ii) the single crystal semiconductor donor substrate comprises twomajor, generally parallel surfaces, one of which is the front surface ofthe semiconductor donor substrate and the other of which is a backsurface of the semiconductor donor substrate, a circumferential edgejoining the front and back surfaces of the semiconductor donorsubstrate, a central plane between the front and back surfaces of thesemiconductor donor substrate, and a bulk region between the front andback surfaces of the semiconductor donor substrate, and further whereinthe single crystal semiconductor donor substrate comprises a cleaveplane; and annealing the bonded structure at a temperature and for aduration sufficient to strengthen the bond between the donor dielectriclayer of the single crystal semiconductor donor substrate and the frontsurface of the single crystal semiconductor handle substrate, whereinannealing occurs at a temperature between about 300° C. and about 700°C., and at a pressure between about 0.5 MPa and about 200 MPa.

The present invention is still further directed to a method of preparinga multilayer structure, the method comprising: bonding a donordielectric layer on a front surface of a single crystal semiconductordonor substrate to a handle dielectric layer on a front surface of asingle crystal semiconductor handle substrate to thereby form a bondedstructure, wherein (i) the single crystal semiconductor handle substratecomprises two major, generally parallel surfaces, one of which is thefront surface of the single crystal semiconductor handle substrate andthe other of which is a back surface of the single crystal semiconductorhandle substrate, a circumferential edge joining the front surface andthe back surface of the single crystal semiconductor handle substrate, acentral plane between the front surface and the back surface of thesingle crystal semiconductor handle substrate, and a bulk region betweenthe front and back surfaces of the single crystal semiconductor handlesubstrate and (ii) the single crystal semiconductor donor substratecomprises two major, generally parallel surfaces, one of which is thefront surface of the semiconductor donor substrate and the other ofwhich is a back surface of the semiconductor donor substrate, acircumferential edge joining the front and back surfaces of thesemiconductor donor substrate, a central plane between the front andback surfaces of the semiconductor donor substrate, and a bulk regionbetween the front and back surfaces of the semiconductor donorsubstrate, and further wherein the single crystal semiconductor donorsubstrate comprises a cleave plane; and annealing the bonded structureat a temperature and for a duration sufficient to strengthen the bondbetween the donor dielectric layer of the single crystal semiconductordonor substrate and the front surface of the single crystalsemiconductor handle substrate, wherein annealing occurs at atemperature between about 300° C. and about 700° C., and at a pressurebetween about 0.5 MPa and about 200 MPa.

Other objects and features will be in part apparent and in part pointedout hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A through 1C depict a process flow according to some embodimentsof the present invention.

FIG. 2 depicts a multilayer structure according to some embodiments ofthe present invention.

FIG. 3 depicts a multilayer structure according to some embodiments ofthe present invention.

FIGS. 4A and 4B depicts structures of exemplary flowable silazanes.

FIG. 5 depicts an exemplary structure of a flowable silsesquioxane.

DETAILED DESCRIPTION OF THE EMBODIMENT(S) OF THE INVENTION

The present invention is directed to a multi-layeredsemiconductor-on-insulator structure (SOI, e.g., a silicon-on-insulatorstructure) that resists impurities contained in a handle substrate fromhaving an influence on the device. The dielectric layer in thesemiconductor-on-insulator structure may comprise one or more insulatinglayers located between the handle substrate and the donor substrate ordevice layer. The one or more insulating layers in the SOI structureaccording to the present invention may include silicon nitride, siliconoxide, silicon oxynitride, and combinations of these materials.Preferably, the dielectric layer comprises a multilayer comprising atleast two insulating layers comprising these materials, or at leastthree insulating layers, or more insulating layers. According to someembodiments of the present invention, the insulating layer may comprisesan oxide-nitride-oxide dielectric (ONO) in which an oxide layer ininterfacial contact with the handle substrate an a second oxide layer isin interfacial contact with the donor substrate or device layer. Thenitride layer is between the two oxide layers.

In a multi-layered semiconductor-on-insulator structure (SOI, e.g., asilicon on insulator structure) comprising an oxide-nitride-oxidedielectric layer (ONO), the buried oxide under the nitride may not bepresent in the final device. Therefore, process steps that are newlyavailable in the deposition, treatment, and integration can reduce thecost and facilitate customer manufacturing.

According to some embodiments of the present disclosure, a method isprovided to create an oxide layer in an SOI structure, preferably, anoxide layer in an ONO multilayer structure. By depositing a flowableoxide or oxide capable or low temperature reflow, the implanted donorroughness or flatness will be mitigated after bonding. The purpose ofthis method is to improve reliability and reduce cost of multilayer SOIstructures. If the oxide underlayer flows, bond voids and interfacedefect sensitivity can be reduced.

According to some embodiments of the present disclosure, a method isprovided to optimize layer transfer (e.g., by lessened dependence onsurface energy and flatness/roughness, reduced voids, increased bondstrength, prevention of autocleave, and reduced terrace width) by makinguse of pressurized bond treatment and/or pressurized post cleave anneal.The purpose of this method is to improve reliability of transfer,improve bond properties, and prevent thermal cleave.

I. Semiconductor Handle Substrate and Semiconductor Donor Substrate

The substrates for use in the present invention include a semiconductorhandle substrate, e.g., a single crystal semiconductor handle wafer anda semiconductor donor substrate, e.g., a single crystal semiconductordonor wafer. The semiconductor device layer in asemiconductor-on-insulator composite structure is derived from thesingle crystal semiconductor donor wafer. The semiconductor device layermay be transferred onto the semiconductor handle substrate by waferthinning techniques such as etching a semiconductor donor substrate orby cleaving a semiconductor donor substrate comprising a damage plane.According to the method of the present invention, one or more insulatinglayers may be prepared on the surfaces of either or both the singlecrystal semiconductor handle wafer and the single crystal semiconductordonor wafer.

FIGS. 1A through 1C, FIG. 2, and FIG. 3 depict a process flow accordingto some embodiments of the present invention. With reference to FIG. 1A,an exemplary, non-limiting single crystal semiconductor handle substrateor wafer 100 is depicted. In general, the single crystal semiconductorhandle wafer 100 comprises two major, generally parallel surfaces. Oneof the parallel surfaces is a front surface 102 of the single crystalsemiconductor handle wafer 100, and the other parallel surface is a backsurface 104 of the single crystal semiconductor handle wafer 100. Thesingle crystal semiconductor handle wafer 100 comprises acircumferential edge 106 joining the front and back surfaces 102, 104.The single crystal semiconductor handle wafer 100 comprise a centralaxis 108 perpendicular to the two major, generally parallel surfaces102, 104 and also perpendicular to a central plane defined by the pointsmidway between the front and back surfaces 102, 104. The single crystalsemiconductor handle wafer 100 comprises a bulk region 110 between thetwo major, generally parallel surfaces 102, 104. Since semiconductorwafers, e.g., silicon wafers, typically have some total thicknessvariation (TTV), warp, and bow, the midpoint between every point on thefront surface 102 and every point on the back surface 104 may notprecisely fall within a plane. As a practical matter, however, the TTV,warp, and bow are typically so slight that to a close approximation themidpoints can be said to fall within an imaginary central plane which isapproximately equidistant between the front and back surfaces 102, 104.

Prior to any operation as described herein, the front surface 102 andthe back surface 104 of the single crystal semiconductor handle wafer100 may be substantially identical. A surface is referred to as a “frontsurface” or a “back surface” merely for convenience and generally todistinguish the surface upon which the operations of method of thepresent invention are performed. In the context of the presentinvention, a “front surface” of a single crystal semiconductor handlewafer 100, e.g., a single crystal silicon handle wafer, refers to themajor surface of the substrate that becomes an interior surface of thebonded structure. Accordingly, a “back surface” of a single crystalsemiconductor handle wafer 100, e.g., a handle wafer, refers to themajor surface that becomes an exterior surface of the bonded structure.Similarly, a “front surface” of a single crystal semiconductor donorsubstrate, e.g., a single crystal silicon donor wafer, refers to themajor surface of the single crystal semiconductor donor substrate thatbecomes an interior surface of the bonded structure, and a “backsurface” of a single crystal semiconductor donor substrate, e.g., asingle crystal silicon donor wafer, refers to the major surface thatbecomes an exterior surface of the bonded structure. In the context ofthe present invention, one or more insulating layers may be prepared onthe front surfaces of either or both the single crystal semiconductorhandle substrate 100 and the single crystal semiconductor donorsubstrate. Upon completion of conventional bonding and wafer thinningsteps, the single crystal semiconductor donor substrate forms thesemiconductor device layer of the semiconductor-on-insulator (e.g.,silicon-on-insulator) composite structure.

The single crystal semiconductor handle substrate and the single crystalsemiconductor donor substrate may be single crystal semiconductorwafers. In preferred embodiments, the semiconductor wafers comprise amaterial selected from the group consisting of silicon, silicon carbide,silicon germanium, gallium arsenide, gallium nitride, indium phosphide,indium gallium arsenide, germanium, and combinations thereof. The singlecrystal semiconductor wafers, e.g., the single crystal silicon handlewafer and single crystal silicon donor wafer, of the present inventiontypically have a nominal diameter of at least about 150 mm, at leastabout 200 mm, at least about 300 mm, or at least about 450 mm. Waferthicknesses may vary from about 250 micrometers to about 1500micrometers, such as between about 300 micrometers and about 1000micrometers, suitably within the range of about 500 micrometers to about1000 micrometers. In some specific embodiments, the wafer thickness maybe about 725 micrometers. In some embodiments, the wafer thickness maybe about 775 micrometers.

In particularly preferred embodiments, the single crystal semiconductorwafers comprise single crystal silicon wafers which have been slicedfrom a single crystal ingot grown in accordance with conventionalCzochralski crystal growing methods or float zone growing methods. Suchmethods, as well as standard silicon slicing, lapping, etching, andpolishing techniques are disclosed, for example, in F. Shimura,Semiconductor Silicon Crystal Technology, Academic Press, 1989, andSilicon Chemical Etching, (J. Grabmaier ed.) Springer-Verlag, N.Y., 1982(incorporated herein by reference). Preferably, the wafers are polishedand cleaned by standard methods known to those skilled in the art. See,for example, W. C. O'Mara et al., Handbook of Semiconductor SiliconTechnology, Noyes Publications. If desired, the wafers can be cleaned,for example, in a standard SC1/SC2 solution. In some embodiments, thesingle crystal silicon wafers of the present invention are singlecrystal silicon wafers which have been sliced from a single crystalingot grown in accordance with conventional Czochralski (“Cz”) crystalgrowing methods, typically having a nominal diameter of at least about150 mm, at least about 200 mm, at least about 300 mm, or at least about450 mm. Preferably, both the single crystal silicon handle wafer and thesingle crystal silicon donor wafer have mirror-polished front surfacefinishes that are free from surface defects, such as scratches, largeparticles, etc. Wafer thickness may vary from about 250 micrometers toabout 1500 micrometers, such as between about 300 micrometers and about1000 micrometers, suitably within the range of about 500 micrometers toabout 1000 micrometers. In some specific embodiments, the waferthickness may be between about 725 micrometers and about 800micrometers, such as between about 750 micrometers and about 800micrometers. In some embodiments, the wafer thickness may be about 725micrometers. In some embodiments, the wafer thickness may be about 775micrometers.

In some embodiments, the single crystal semiconductor wafers, i.e.,single crystal semiconductor handle wafer and single crystalsemiconductor donor wafer, comprise interstitial oxygen inconcentrations that are generally achieved by the Czochralski-growthmethod. In some embodiments, the single crystal semiconductor waferscomprise oxygen in a concentration between about 4 PPMA and about 18PPMA. In some embodiments, the semiconductor wafers comprise oxygen in aconcentration between about 10 PPMA and about 35 PPMA. In someembodiments, the single crystal silicon wafer comprises oxygen in aconcentration of no greater than about 10 PPMA. Interstitial oxygen maybe measured according to SEMI MF 1188-1105.

The single crystal semiconductor handle wafer 100 may have anyresistivity obtainable by the Czochralski or float zone methods.Accordingly, the resistivity of the single crystal semiconductor handlewafer 100 is based on the requirements of the end use/application of thestructure of the present invention. The resistivity may therefore varyfrom milliohm or less to megaohm or more. In some embodiments, thesingle crystal semiconductor handle wafer 100 comprises a p-type or ann-type dopant. Suitable dopants include boron (p type), gallium (ptype), phosphorus (n type), antimony (n type), and arsenic (n type). Thedopant concentration is selected based on the desired resistivity of thehandle wafer. In some embodiments, the single crystal semiconductorhandle substrate comprises a p-type dopant. In some embodiments, thesingle crystal semiconductor handle substrate is a single crystalsilicon wafer comprising a p-type dopant, such as boron.

In some embodiments, the single crystal semiconductor handle wafer 100has a relatively low minimum bulk resistivity, such as below about 100ohm-cm, below about 50 ohm-cm, below about 1 ohm-cm, below about 0.1ohm-cm, or even below about 0.01 ohm-cm. In some embodiments, the singlecrystal semiconductor handle substrate 100 has a relatively low minimumbulk resistivity, such as below about 100 ohm-cm, or between about 1ohm-cm and about 100 ohm-cm. Low resistivity wafers may compriseelectrically active dopants, such as boron (p type), gallium (p type),aluminum (p type), indium (p type), phosphorus (n type), antimony (ntype), and arsenic (n type).

In some embodiments, the single crystal semiconductor handle wafer 100has a relatively high minimum bulk resistivity. High resistivity wafersare generally sliced from single crystal ingots grown by the Czochralskimethod or float zone method. High resistivity wafers may compriseelectrically active dopants, such as boron (p type), gallium (p type),aluminum (p type), indium (p type), phosphorus (n type), antimony (ntype), and arsenic (n type), in generally very low concentrations.Cz-grown silicon wafers may be subjected to a thermal anneal at atemperature ranging from about 600° C. to about 1000° C. in order toannihilate thermal donors caused by oxygen that are incorporated duringcrystal growth. In some embodiments, the single crystal semiconductorhandle wafer has a minimum bulk resistivity of at least 100 Ohm-cm, oreven at least about 500 Ohm-cm, such as between about 100 Ohm-cm andabout 100,000 Ohm-cm, or between about 500 Ohm-cm and about 100,000Ohm-cm, or between about 1000 Ohm-cm and about 100,000 Ohm-cm, orbetween about 500 Ohm-cm and about 10,000 Ohm-cm, or between about 750Ohm-cm and about 10,000 Ohm-cm, between about 1000 Ohm-cm and about10,000 Ohm-cm, between about 1000 Ohm-cm and about 6000 ohm-cm, betweenabout 2000 Ohm-cm and about 10,000 Ohm-cm, between about 3000 Ohm-cm andabout 10,000 Ohm-cm, or between about 3000 Ohm-cm and about 5,000Ohm-cm. In some preferred embodiments, the single crystal semiconductorhandle substrate has a bulk resistivity between about 1000 Ohm-cm andabout 6,000 Ohm-cm. Methods for preparing high resistivity wafers areknown in the art, and such high resistivity wafers may be obtained fromcommercial suppliers, such as SunEdison Semiconductor Ltd. (St. Peters,Mo.; formerly MEMC Electronic Materials, Inc.).

The single crystal semiconductor handle wafer 100 may comprise singlecrystal silicon. The single crystal semiconductor handle wafer 100 mayhave, for example, any of (100), (110), or (111) crystal orientation,and the choice of crystal orientation may be dictated by the end use ofthe structure.

Optionally, the front surface 102, the back surface 104, or both may beoxidized according to methods known in the art. Oxidation may beaccomplished by means known in the art, such as thermal oxidation (inwhich some portion of the deposited semiconductor material film will beconsumed) or CVD oxide deposition. The oxidation layer on the frontsurface 102, the back surface 104, or both may be at least about 1nanometer thick, such as between about 10 nanometers and about 5000nanometers thick, such as between about 100 nanometers and about 1000nanometers, or between about 200 nanometers and about 400 nanometers. Insome embodiments, the oxidation layer is relatively thin, such asbetween about 5 angstroms and about 25 angstroms, such as between about10 angstroms and about 15 angstroms. Thin oxide layers can be obtainedby exposure to a standard cleaning solution, such as an SC1/SC2 cleaningsolution. In some embodiments, the SC1 solution comprises 5 partsdeioinized water, 1 part aqueous (ammonium hydroxide, 29% by weight ofNH₃), and part of aqueous H₂O₂ (hydrogen peroxide, 30%). In someembodiments, the handle substrate may be oxidized by exposure to anaqueous solution comprising an oxidizing agent, such as an SC2 solution.In some embodiments, the SC2 solution comprises 5 parts deioinizedwater, 1 part aqueous HCl (hydrochloric acid, 39% by weight), and 1 partof aqueous H₂O₂ (hydrogen peroxide, 30%).

II. Dielectric Layer Comprising One or More Insulating Layers

According to the method of the present invention, and with reference toFIG. 2, a dielectric layer 420 comprising one or more insulating layers(e.g., three or more insulating layers, therein numbers 200, 300, and400) is prepared between a single crystal semiconductor handle substrate100 and a single crystal semiconductor donor substrate 500. Withreference to FIG. 2, a non-limiting, exemplary multi-layeredsemiconductor-on-insulator structure (SOI, e.g., a silicon on insulatorstructure) is depicted. According to FIG. 2, the SOI structure comprisesa dielectric layer 420 comprising three insulating layers, e.g., anoxide-nitride-oxide dielectric layer (ONO), according to someembodiments of the present invention. In some embodiments, themulti-layered semiconductor-on-insulator structure comprises a singlecrystal semiconductor handle substrate 100, a first semiconductor oxidelayer 200, a semiconductor nitride layer 300, a second semiconductoroxide layer 400, and a single crystal semiconductor donor substrate 500.Other configurations of insulating layers fall within the scope of thepresent disclosure. For example, one or more insulating layers may beexcluded from the dielectric layer, or additional insulating layers maybe included. With reference to FIG. 2, the bonding interface can be anyof the following: (1) between the first semiconductor oxide layer 200and the semiconductor nitride layer 300, (2) between the semiconductornitride layer 300 and the semiconductor second oxide layer 400, and (3)between the first semiconductor oxide layer 200 and the secondsemiconductor oxide layer 400 if the structure lacks a nitride layer.

The dielectric layer 420 may comprise the ONO layers as depicted in FIG.2, or may comprise other structures comprising one or more layers ofinsulating material. The dielectric layer 420 may be formed upon thefront surface of the single crystal semiconductor handle substrate 100or it may be formed upon the front surface of the single crystalsemiconductor donor substrate 500. In still further embodiments,portions of the dielectric layer 420 may be contributed by insulatinglayers formed upon both the front surface of the single crystalsemiconductor handle substrate 100 and the front surface of the singlecrystal semiconductor donor substrate 500.

The dielectric layer according to the present invention may compriseinsulating materials selected from among silicon dioxide, siliconnitride, silicon oxynitride, hafnium oxide, titanium oxide, zirconiumoxide, lanthanum oxide, barium oxide, and any combination thereof. Insome embodiments, the dielectric layer comprises one or more insulatingmaterial selected from the group consisting of silicon dioxide, siliconnitride, silicon oxynitride, and any combination thereof. In someembodiments, the dielectric layer has a thickness of at least about 10nanometer thick, such as between about 10 nanometers and about 10,000nanometers, between about 10 nanometers and about 5,000 nanometers,between 50 nanometers and about 400 nanometers, or between about 100nanometers and about 400 nanometers, such as about 50 nanometers, 100nanometers, or 200 nanometers.

In some embodiments, the dielectric layer 420 comprises multiple layersof insulating material, for example, as depicted in FIG. 2, althoughother configurations are within the scope of this invention.

The dielectric layer may comprise two insulating layers, threeinsulating layers, or more. Each insulating layer may comprise amaterial selected from among silicon dioxide, silicon oxynitride,silicon nitride, hafnium oxide, titanium oxide, zirconium oxide,lanthanum oxide, barium oxide, and any combination thereof. In someembodiments, each insulating layer may comprise a material selected fromthe group consisting of silicon dioxide, silicon nitride,siliconoxynitride, and any combination thereof. Each insulating layermay have a thickness of at least about 10 nanometer thick, such asbetween about 10 nanometers and about 10,000 nanometers, between about10 nanometers and about 5,000 nanometers, between 50 nanometers andabout 400 nanometers, or between about 100 nanometers and about 400nanometers, such as about 50 nanometers, 100 nanometers, or 200nanometers.

In some embodiments, the dielectric layer comprises two insulatinglayers, wherein the two insulating layers comprise silicon dioxidelayer, silicon nitride, silicon oxynitride, or any combination thereof.In some embodiments, the dielectric layer comprises two insulatinglayers prepared upon the front surface of a single crystal semiconductordonor substrate. For example, the two layers comprise a silicon dioxidelayer in interfacial contact with the front surface of the singlecrystal semiconductor donor substrate (before the cleaving process) orthe single crystal semiconductor device layer (after the cleavingprocess) and a silicon nitride layer in interfacial contact with thesilicon dioxide layer. In some embodiments, the dielectric layercomprises two insulating layers prepared upon the front surface of asingle crystal semiconductor handle substrate. In some embodiments, thedielectric layer comprises two insulating layers, one of which isprepared upon the front surface of a single crystal semiconductor handlesubstrate, and the other of which is prepared upon the front surface ofa single crystal semiconductor donor substrate. Each insulating layerwithin a bilayer dielectric layer may have a thickness of at least about10 nanometer thick, such as between about 10 nanometers and about 10,000nanometers, between about 10 nanometers and about 5,000 nanometers,between 50 nanometers and about 400 nanometers, or between about 100nanometers and about 400 nanometers, such as about 50 nanometers, 100nanometers, or 200 nanometers.

In some embodiments, and as depicted in FIG. 2, the dielectric layer 420comprises three insulating layers. In some embodiments, the threeinsulating layers comprise a silicon dioxide layer, a silicon nitridelayer in interfacial contact with the silicon dioxide layer, and asilicon dioxide layer in interfacial contact with the silicon nitridelayer. In some embodiments, the dielectric layer comprises threeinsulating layers prepared upon the front surface of a single crystalsemiconductor donor substrate. For example, the dielectric layer 420comprises three insulating layers, wherein the three insulating layerscomprise a silicon dioxide layer in interfacial contact with the frontsurface of the single crystal semiconductor donor substrate (before thecleaving process) or the single crystal semiconductor device layer(after the cleaving process), a silicon nitride layer in interfacialcontact with the silicon dioxide layer, and a silicon dioxide layer ininterfacial contact with the silicon nitride layer. In some embodiments,the dielectric layer comprises three insulating layers prepared upon thefront surface of a single crystal semiconductor handle substrate. Insome embodiments, the dielectric layer comprises three insulatinglayers, one or two of which are prepared upon the front surface of asingle crystal semiconductor handle substrate, and the other one or twoof which are prepared upon the front surface of a single crystalsemiconductor donor substrate. Each insulating layer within a trilayerdielectric layer may have a thickness of at least about 10 nanometerthick, such as between about 10 nanometers and about 10,000 nanometers,between about 10 nanometers and about 5,000 nanometers, between 50nanometers and about 400 nanometers, or between about 100 nanometers andabout 400 nanometers, such as about 50 nanometers, 100 nanometers, or200 nanometers.

III. Flowable Insulating Layer and Reflowable Insulating Layer

In some embodiments, and with reference to FIGS. 1A and 1B, at least aportion, i.e., one, two, three or more insulating layers, of thedielectric layer is formed upon the front surface 102 of the singlecrystal semiconductor handle substrate 100. In some embodiments, aninsulating layer 120 comprising a flowable or reflowable material isdeposited upon the front surface 102 of the single crystal semiconductorhandle substrate 100. In some embodiments, and with reference to FIG.1C, an additional insulating layer 140, which may be an oxide layer, anoxynitride layer, or a nitride layer, may be deposited upon theinsulating layer 120 comprising a flowable or reflowable material. Inother embodiments, the handle substrate 100 comprising the insulatinglayer 120 comprising a flowable or reflowable material is not subjectedto further deposition, and the insulating layer 120 comprising aflowable or reflowable material is useful as the bonding interface,thereby taking advantage of the flowable or reflowable insulatinglayer's planarizing properties, which reduces roughness/voids in thebonding region. In still further embodiments, the flowable or reflowablematerial may be deposited on the front surface of the single crystalsemiconductor donor substrate.

In some embodiments, an insulating layer comprising a reflowablematerial is deposited upon the front surface 102 of the single crystalsemiconductor handle substrate 100. A reflowable insulating layercomprises a material capable of flowing at a temperature of less thanabout 1000° C. A curing step may be employed in order to smooth andplanarize an insulating layer comprising a reflowable material.Reflowable behavior of films occurs due to heating the layer afterdeposition for void free planarization. Doped films are a common way tolower the glass transition temperature. By allowing the film to “reflow”at high temperatures, voids may disappear, and bond strength due to theadded contact is expected.

In some embodiments, an insulating layer comprising a flowable materialis deposited upon the front surface 102 of the single crystalsemiconductor handle substrate 100. A flowable insulating layer tends tosmooth and planarize during its deposition and reduce roughness. Basedon the geometry of the material, the thickness of deposited filmchanges. Generally, surface tension dictates that the film will bethicker at concave geometries and thinner at convex areas. Flowablefilms may be deposited by solvent based spin on, or low temperaturecondensation reactions. Flowable films have the unique ability toplanarize features and reduce roughness. In some embodiments, theflowable insulating layer comprises a flowable oxide. Flowable oxidesinclude polymer precursors that have been dissolved or functionalized.By virtue of the solution or the activity of the polymer once deposited,it has the ability to move on the wafer surface. Two general applicationtechniques are used, spin on dielectrics or CVD.

In some embodiments, the flowable insulating layer comprises a flowablesilazane. Polysilazanes are polymers that comprise a polymer backbonecomprising generally alternating silicon and nitrogen atoms. Flowablesilazanes may be cured to remove NH₃ when pure undoped silica glass isrequired. Suitable dissolved polysilazane materials may be acquired fromAZ Electronic Materials, Dow Chemical, and Sigma Aldrich. A suitablespin on tool may be acquired from Tokyo Electron Limited. Subsequentcuring and annealing is common after deposition of the flowablesilazane. Structures of exemplary flowable silazanes are depicted inFIGS. 4A and 4B. FIG. 4A depicts a non-derivatized flowable silazane. Ifall substituents R are H atoms, the polymer is designated asPerhydropolysilazane, Polyperhydridosilazane or Inorganic Polysilazane([H₂Si—NH]n). FIG. 4B depicts a flowable silazane derivatized with Rgroups. In some embodiments, the R group comprises hydrocarbyl havingfrom one to 12 carbon atoms, such as alkyl groups having from one to 12carbon atoms, e.g., methyl, ethyl, n-propyl, isopropyl, butyl, etc. Insome embodiments, the R group comprises aromatic groups having fromthree to 12 carbon atoms, e.g., phenyl, naphthyl, etc.

In some embodiments, the flowable insulating layer comprises a flowablesilsesquioxane. Silsesquioxanes are flowable silicon oxides. Asilsesquioxane is an organosilicon compound with the chemical formula[RSiO₃/2]n (R=H, alkyl, aryl or alkoxyl). In some embodiments, the Rgroup comprises hydrocarbyl having from one to 12 carbon atoms, such asalkyl groups having from one to 12 carbon atoms, e.g., methyl, ethyl,n-propyl, isopropyl, butyl, etc. In some embodiments, the R groupcomprises alkoxy from one to 12 carbon atoms, e.g., methoxy, ethoxy,n-propoxy, isopropoxy, butoxy, etc. In some embodiments, the R groupcomprises aromatic groups having from three to 12 carbon atoms, e.g.,phenyl, naphthyl, etc. Silsesquioxanes are colorless solids that adoptcage-like or polymeric structures with Si—O—Si linkages and tetrahedralSi vertices. Silsesquioxanes are known in molecular form with 6, 8, 10,and 12 Si vertices, as well as polymers. The cages are sometimes labeledT6 T8, T10, and T12, respectively (T=tetrahedral vertex). They aregenerally available as hydrogen silsesquioxane in a carrier solvent suchas ketones or siloxane. Suitable silsesquioxane may be sourced from DowCorning and Sigma Aldrich. A suitable spin on tool may be acquired fromTokyo Electron Limited. A structure of an exemplary flowablesilsesquioxane is depicted in FIG. 5.

In some embodiments, a reflowable insulating layer comprises a dopedoxide. In some embodiments, reflowable insulating layer comprises asilicate glass selected from the group consisting of phosphosilicateglass, borosilicate glass, borophosphosilicate glass (BPSG), and anycombination thereof. Doped glasses are common in the industry to lowerthe glass transition temperature. By allowing the film to “reflow” athigh temperatures, one may fill small voids or gaps.

In some embodiments, an insulating layer 120 comprising a flowable orreflowable material is deposited by contacting the front surface of thesingle crystal semiconductor handle substrate with a solution comprisingoxide precursor and/or non-oxide precursor. For example, silsesquioxanesare commonly prepared from hydrolytic condensation reactions oftrifunctional organosilicon monomers, e.g., RSiCl₃ or RSi(OMe)₃. Variousalternatives are available with different structures or functionalmodification with organics. Silazanes are commonly available asmonomers, and also offer the potential to be converted to oxide. Thereare also precursors commercially available for other nitrides, carbides,and borides. In some embodiments, the insulating layer 120 comprising aflowable or reflowable material has a thickness between about 50nanometers and about 1 micrometer, between about 100 nanometers andabout 1 micrometer.

IV. Curing the Flowable or Reflowable Insulating Layer

An insulating layer 120 comprising a flowable or reflowable material maybe annealed to thereby reflow, cure, and/or densify the film. Bothflowable and reflow films can be densified. Only reflowable films flowduring an anneal. During densification of a reflowable insulating layer,such as doped oxides (like borophosphosilicate glass, BPSG), theyreflow. Advantageously, reflow of a reflowable material can smooth thesurface, thereby decreasing surface roughness and rendering the surfacemore amenable to bonding.

Flowable polymers only flow during deposition, and a subsequent curelocks it into place. Curing a flowable insulating layer may causedensification in the range of between about 5% and about 20%.Densification anneals may not change the thickness of measurement ofdensity, but is usually used to chemically change the film, therebymaking resistant to chemical etch. A flowable oxide insulating layer maybe cured to remove residual solvent from the spin on process.Additionally, an as-deposited layer may be reactive after deposition,and a cure may redistribute NH, SiN, Si—O and Si—H bonds. The reactionmechanism responsible for the chemical changes is induced by heating invarious ambient atmospheres, generally an oxidizing atmosphere. Curingof flowables is accompanied by weight loss, density, and change indielectric properties. For certain applications, one might be interestedin densification until it is very similar to thermal oxide.

In some embodiments, curing of the insulating layer 120 comprising aflowable or reflowable material may occur by contacting the layer withozone. The ozone may be dissolved in water, or the insulating layer 12may be exposed to an ozone containing ambient atmosphere. In someembodiments, curing of an insulating layer 120 comprising a flowable orreflowable material may occur by irradiating the layer with ultravioletlight, such as light having a wavelength between about 185 nanometersand about 256 nanometers, depending upon the composition of theinsulating layer. In some embodiments, an insulating layer 120comprising a flowable or reflowable material is cured by annealing thesingle crystal semiconductor handle substrate having the insulatinglayer on the front surface thereof, for example at a temperature betweenabout 800° C. and about 1000° C., depending upon the composition of theinsulating layer and the dopant concentration.

Cure and/or densification of the insulating layer 120 comprising aflowable or reflowable material may decrease the surface roughness. Thesurface roughness according to the root mean square method over a 2micrometer by 2 micrometer surface area, RMS_(2×2 um2), is preferablyless than about 2 angstroms, such as between about 1 angstrom and about2 angstroms, wherein root mean squared is calculated according to thefollowing equation:

$R_{q} = \sqrt{\frac{1}{n}{\sum\limits_{i = 1}^{n}y_{i}^{2}}}$

The roughness profile contains ordered, equally spaced points along thetrace, and y_(i) is the vertical distance from the mean line to the datapoint. At a surface roughness of preferably less than 2 angstroms, thesurface is ready for bonding or optional oxidation.

V. Plasma Deposition of Insulating Layers

In some embodiments, one or more insulating layers may be prepared uponthe front surface of the single crystal semiconductor handle substrate100 or upon the front surface of a single crystal semiconductor donorsubstrate by a plasma deposition process, such as plasma enhancedchemical vapor deposition. In some embodiments, an insulating layercomprising a semiconductor oxide (e.g., silicon oxide) is deposited byan oxygen plasma treatment. In some embodiments, an insulating layercomprising a semiconductor nitride (e.g., silicon nitride) is depositedby a nitrogen plasma treatment. In some embodiments, an insulating layercomprising a semiconductor oxynitride (e.g., silicon oxynitride) isdeposited by a plasma treatment comprising nitrogen and oxygenprecursors. A wide variety of substrate configurations may be subjectedto oxygen plasma treatment and/or nitrogen plasma treatment. Withreference to FIG. 1A, the front surface 102 of the single crystalsemiconductor handle substrate 100 may be subjected to oxygen plasmatreatment and/or nitrogen plasma treatment to thereby deposit asemiconductor oxide (e.g., silicon oxide), a semiconductor nitride(e.g., silicon nitride), or a semiconductor oxynitride (e.g., siliconoxynitride). One or more insulating layers may be deposited by plasmadeposition on the front surface 102 of the single crystal semiconductorhandle substrate 100. With reference to FIGS. 1B and 1C, the surface ofan insulating layer 120 comprising a flowable or reflowable material oran insulating layer 140 may be subjected to oxygen plasma treatmentand/or nitrogen plasma treatment to deposit one or more additionalinsulating layers. In still further embodiments of the presentinvention, one or more insulating layers may be deposited upon thesingle crystal semiconductor donor substrate by plasma deposition.

In some embodiments, the oxygen plasma and/or nitrogen plasma surfaceactivation tool is a commercially available tool, such as thoseavailable from EV Group, such as EVG®810LT Low Temp Plasma ActivationSystem. General requirements of a plasma enhanced CVD chamber include areactor with various electrode designs, power generation electronics,impedance matching network to transfer power to the gas load, mass flowcontrollers for input gasses, and pressure control systems. Typicalsystems are vertical tube reactors powered by an inductively coupled RFsource. The single crystal semiconductor handle substrate 100 and/ordonor substrate is loaded into the chamber and placed on a heatedsupport chamber. The chamber is evacuated and backfilled with an oxygengas source and/or a nitrogen gas source in a carrier gas, such as argon,to a pressure less than atmospheric to thereby create the plasma. Oxygenand/or water are suitable source gases for plasma oxide treatment.Ammonia and/or nitrogen and/or nitric oxide (NO) and/or nitrous oxide(N₂O) gas are suitable source gases for plasma nitride treatment.Oxynitride films may be deposited by including oxygen and nitrogen gassources. Additionally, the use of nitric oxide or nitrous oxideadditionally incorporates oxygen in to the insulating layer, therebydepositing an oxynitride film. To deposit a silicon nitride or a siliconoxide plasma film, suitable silicon precursors include methyl silane,silicon tetrahydride (silane), trisilane, disilane, pentasilane,neopentasilane, tetrasilane, dichlorosilane (SiH₂Cl₂), trichlorosilane(SiHCl₃), silicon tetrachloride (SiCl₄), among others. Suitably, Ar isadded as a carrier gas.

In some embodiments, a single crystal semiconductor handle substrate 100or a single crystal silicon donor substrate is subjected to plasmatreatment to deposit and insulating layer comprising semiconductornitride (e.g., silicon nitride) or semiconductor oxynitride (e.g.,silicon oxynitride). The substrates may be subjected to plasmadeposition without any additional layers. Alternatively, one or moreinsulating layers may be deposited upon the substrates, and plasmaenhanced CVD may be used to deposit additional insulating layers uponthe insulating layers deposited according to other techniques.

Plasma deposition may be varied to tune the properties of thesemiconductor nitride (e.g., silicon nitride) or semiconductoroxynitride (e.g., silicon oxynitride). For example, the pressure, flowrate, temperature, and relative ratio of precursors, e.g., ratio of NH₃to N₂O gases, may tune the silicon and nitride molar ratios of theplasma deposited nitride layer. Additionally, inclusion of an oxygenprecursor incorporates oxygen to prepare an oxynitride layer. In someembodiments, plasma deposition may occur in an ambient atmospherecomprising silicon and nitrogen precursors to thereby deposit a siliconnitride layer on the handle substrate and/or donor substrate. After aduration sufficient to deposit nitride, an oxygen precursor may beintroduced into the atmosphere to thereby deposit oxynitride. The oxygenconcentration in the handle semiconductor oxynitride layer may varyaccording to a gradient, whereby the oxygen concentration is low at theinterface with the handle semiconductor nitride layer and increases inthe perpendicular direction away from the surface of the handlesemiconductor oxynitride layer. After a duration sufficient to depositan oxynitride layer, the flow of the nitrogen precursor may be ceasedand deposition may continue only with silicon precursor and an oxygengas source to thereby deposit an insulating layer comprisingsemiconductor oxide, e.g., silicon oxide. In some embodiments, adielectric layer may be deposited by plasma techniques comprising asemiconductor nitride (e.g., silicon nitride) layer and a semiconductoroxynitride (e.g., silicon oxynitride) layer. In some embodiments, adielectric layer may be deposited by plasma techniques comprising asemiconductor nitride (e.g., silicon nitride) layer, a semiconductoroxynitride (e.g., silicon oxynitride) layer, and a semiconductor oxide(e.g., silicon oxide) layer. Advantageously, plasma deposition of adielectric layer comprising multiple insulating layers may occurcontinuously, i.e., without interruption, by varying the ratios andidentities of the process gases.

The plasma deposited semiconductor nitride (e.g., silicon nitride),semiconductor oxynitride (e.g., silicon oxynitride), or semiconductoroxide (e.g., silicon oxide) may be formed at pressures between about0.01 Torr and about 100 Torr, such as between about 0.1 Torr and about 1Torr. Plasma deposition may occur at a temperature between about 20° C.and about 400° C. Insulating layers having a thickness between about 500angstroms and about 10,000 angstroms can be deposited by PECVD at a ratebetween about 100 angstroms/minute and about 1000 angstroms/minute.

The flow rate ratios of the gaseous silicon precursor and the gaseousnitrogen precursor may be between about 1/200 and about 1/50, such asabout 1/100. These ratios may yield a silicon nitride layer having amolar ratio of silicon to nitride of between about 0.7 and about 1.8.Oxygen may be incorporated in the plasma process, by adding an oxygencontaining species such as oxygen or NO. Adding oxygen during plasmadeposition enables the deposition of dielectric layers havingcompositions that vary in a gradient fashion, e.g., the layer maytransition from semiconductor nitride (e.g., silicon nitride) tosemiconductor oxynitride (e.g., silicon oxynitride) of increasing oxygenconcentration to semiconductor oxide (e.g., silicon oxide).

The refractive index of the insulating layers may be tuned in the rangebetween about 1.2 and about 3, such as between about 1.4 and about 2, orbetween about 1.5 and about 2. Post processing anneal and chemical vapordeposition of silicon oxide, SiO₂, is possible to further tune the bondinterface or hydrogen content of the film. The bonding between thehandle substrate and the donor substrate benefits from roughness of lessthan about 5 angstroms, according to the root mean square method over a2 micrometer by 2 micrometer surface area, RMS_(2×2 um2). Generally thiscan be achieved in a plasma deposition with controlled inductivelycoupled plasma and lowering the bias power below the rougheningthreshold. Successful layer transfer has been demonstrated on plasmadeposited films with roughness of about 5 angstroms or less.

Silicon oxynitride comprises a material having a composition that has achemical formula Si_(x)O_(y)N_(z). In its amorphous form, the values ofx, y, and z may vary continuously between SiO₂ (silicon dioxide) andSi₃N₄ (silicon nitride). Accordingly, in a silicon oxynitride layer, thevalues of y and z are both greater than 0. A known crystalline form ofsilicon oxynitride is Si₂ON₂. According to some embodiments, the siliconoxynitride may be deposited in a gradient fashion, such that thecomposition of the film and thus the refractive index of the film mayvary in a gradient fashion. In some embodiments, silicon oxynitride maybe deposited upon a silicon nitride film by the gradual introduction ofan oxygen precursor (e.g., oxygen, water, N₂O) into the plasmadeposition ambient atmosphere, which may comprise a silicon precursorand a nitrogen precursor, e.g., ammonia. The ratio of NH₃:N₂O may bevaried, that is, lowered, during deposition to gradually increase theoxygen content in the silicon oxynitride layer. In some embodiments,after deposition of a gradient silicon oxynitride layer, all nitrogenprecursors are eliminated from the plasma deposition atmosphere, and theatmosphere contains silicon precursors and oxygen precursors, whichenables deposition of a silicon dioxide layer on the silicon oxynitridelayer. According to some embodiments, the refractive index range of thesilicon oxynitride film may vary between 2.0 for silicon nitride and1.45 for silicon dioxide.

Silicon nitride produced from plasma is structurally distinct fromsilicon nitride deposited according to conventional chemical or physicalvapor deposition techniques. Conventional CVD or PVD depositiongenerally results in a silicon nitride layer having a stoichiometry ofSi₃N₄. Plasma processes can be controlled to deposit a film having acomposition such as Si_(x)N_(y)H_(z) depending on the ratios of inputreactant gasses, power level, substrate temperature, and overall reactorpressure. Pathways in a plasma system exist to form Si—N, Si═N and Si═Nbonds. This is due to the fact that plasma energies are a hammer thatproduce Si_(x)H_(z) and N_(y)H_(z) species. For example, the refractiveindex and optical gap change dramatically with the Si/N ratio. At highersilane concentrations, the films become Si rich and may reach an indexof refraction up to 3.0 (compared to 2 for LPCVD). Other properties thatmay be influenced include dielectric constant, breakdown, mechanical,and chemical (etch rate).

VI. Preparation of the Bonded Structure

With reference to FIG. 2, the single crystal semiconductor handlesubstrate 100, e.g. a single crystal semiconductor handle wafer such asa single crystal silicon handle wafer, prepared according to the methoddescribed herein is next bonded to a semiconductor donor substrate 500,e.g., a single crystal semiconductor donor wafer, which is preparedaccording to conventional layer transfer methods. The single crystalsemiconductor donor substrate 500 may be a single crystal semiconductorwafer. In preferred embodiments, the semiconductor wafer comprises amaterial selected from the group consisting of silicon, silicon carbide,silicon germanium, gallium arsenide, gallium nitride, indium phosphide,indium gallium arsenide, germanium, and combinations thereof. Dependingupon the desired properties of the final integrated circuit device, thesingle crystal semiconductor (e.g., silicon) donor wafer 500 maycomprise electrically active dopants, such as boron (p type), gallium (ptype), aluminum (p type), indium (p type), phosphorus (n type), antimony(n type), and arsenic (n type). The resistivity of the single crystalsemiconductor (e.g., silicon) donor wafer may range from 1 to 50 Ohm-cm,typically, from 5 to 25 Ohm-cm. The single crystal semiconductor donorwafer 500 may be subjected to standard process steps includingoxidation, implant, and post implant cleaning. Accordingly, asemiconductor donor substrate 500, such as a single crystalsemiconductor wafer of a material that is conventionally used inpreparation of multilayer semiconductor structures, e.g., a singlecrystal silicon donor wafer, that has been etched and polished andoptionally oxidized, is subjected to ion implantation to form a damagelayer in the donor substrate.

In some embodiments, the single crystal semiconductor donor substrate500 comprises a dielectric layer. The dielectric layer may comprise oneor more insulating layers formed on the front surface of the singlecrystal semiconductor donor substrate 500. In some embodiments, thedielectric layer 420 comprises multiple layers of insulating material,for example, as depicted in FIG. 2, although other configurations arewithin the scope of this invention. Each insulating layer may comprise amaterial selected from among silicon dioxide, silicon nitride, hafniumoxide, titanium oxide, zirconium oxide, lanthanum oxide, barium oxide,and a combination thereof. In some embodiments, each insulating layermay comprise a material selected from the group consisting of silicondioxide, silicon nitride, and siliconoxynitride. Each insulating layermay have a thickness of at least about 10 nanometer thick, such asbetween about 10 nanometers and about 10,000 nanometers, between about10 nanometers and about 5,000 nanometers, between 50 nanometers andabout 400 nanometers, or between about 100 nanometers and about 400nanometers, such as about 50 nanometers, 100 nanometers, or 200nanometers. As depicted in FIG. 2, the dielectric layer 420 comprisesthree layers. One, two, or three of the layers may be formed upon thesingle crystal semiconductor handle substrate 100. One, two, or three ofthe layers may be formed upon the single crystal semiconductor donorsubstrate 500. Still further, one or two of the layers may be formedupon the single crystal semiconductor handle substrate 100, and one ortwo of the layers may be formed upon the single crystal semiconductordonor substrate 500.

In some embodiments, the front surface of the single crystalsemiconductor donor substrate 500 (e.g., a single crystal silicon donorsubstrate) may be thermally oxidized (in which some portion of thedeposited semiconductor material film will be consumed) to prepare thesemiconductor oxide film, or the semiconductor oxide (e.g., silicondioxide) film may be grown by CVD oxide deposition. In some embodiments,the front surface of the single crystal semiconductor donor substrate500 may be thermally oxidized in a furnace such as an ASM A400 in thesame manner described above. In some embodiments, the single crystalsemiconductor donor substrate 500 is oxidized to provide an oxide layeron the front surface layer of at least about 1 nanometer thick, about 10nanometer thick, such as between about 10 nanometers and about 10,000nanometers, between about 10 nanometers and about 5,000 nanometers, orbetween about 100 nanometers and about 400 nanometers. In someembodiments, the oxidation layer on the single crystal semiconductordonor substrate 500 is relatively thin, such as between about 5angstroms and about 25 angstroms, such as between about 10 angstroms andabout 15 angstroms. Thin oxide layers can be obtained by exposure to astandard cleaning solution, such as an SC1/SC2 cleaning solution.

Ion implantation may be carried out in a commercially availableinstrument, such as an Applied Materials Quantum II, a Quantum LEAP, ora Quantum X. Implanted ions include He, H, H₂, or combinations thereof.Ion implantation is carried out as a density and duration sufficient toform a damage layer in the semiconductor donor substrate. Implantdensity may range from about 10¹² ions/cm² to about 10¹⁷ ions/cm², suchas from about 10¹⁴ ions/cm² to about 10¹⁷ ions/cm², such as from about10¹⁵ ions/cm² to about 10¹⁶ ions/cm². Implant energies may range fromabout 1 keV to about 3,000 keV, such as from about 10 keV to about 3,000keV. Implant energies may range from about 1 keV to about 3,000 keV,such as from about 5 keV to about 1,000 keV, or from about 5 keV toabout 200 keV, or from 5 keV to about 100 keV, or from 5 keV to about 80keV. The depth of implantation determines the thickness of the singlecrystal semiconductor device layer in the final SOI structure. The ionsmay be implanted to a depth between about 100 angstroms and about 30,000angstroms, such as between about 200 angstroms and about 20,000angstroms, such as between about 2000 angstroms and about 15,000angstroms, or between about 15,000 angstroms and about 30,000 angstroms.In some embodiments it may be desirable to subject the single crystalsemiconductor donor wafers, e.g., single crystal silicon donor wafers,to a clean after the implant. In some preferred embodiments, the cleancould include a Piranha clean followed by a DI water rinse and SC1/SC2cleans.

In some embodiments of the present invention, the single crystalsemiconductor donor substrate 500 having an ion implant region thereinformed by He⁺, H⁺, H₂ ⁺, and any combination thereof ion implant isannealed at a temperature sufficient to form a thermally activatedcleave plane in the single crystal semiconductor donor substrate. Anexample of a suitable tool might be a simple Box furnace, such as a BlueM model. In some preferred embodiments, the ion implanted single crystalsemiconductor donor substrate is annealed at a temperature of from about200° C. to about 350° C., from about 225° C. to about 325° C.,preferably about 300° C. Thermal annealing may occur for a duration offrom about 2 hours to about 10 hours, such as from about 2 hours toabout 8 hours. Thermal annealing within these temperatures ranges issufficient to form a thermally activated cleave plane. After the thermalanneal to activate the cleave plane, the single crystal semiconductordonor substrate surface is preferably cleaned.

In some embodiments, the ion-implanted and optionally cleaned andoptionally annealed single crystal semiconductor donor substrate issubjected to oxygen plasma and/or nitrogen plasma surface activation. Insome embodiments, the oxygen plasma surface activation tool is acommercially available tool, such as those available from EV Group, suchas EVG®810LT Low Temp Plasma Activation System. The ion-implanted andoptionally cleaned single crystal semiconductor donor wafer is loadedinto the chamber. The chamber is evacuated and backfilled with O₂ to apressure less than atmospheric to thereby create the plasma. The singlecrystal semiconductor donor wafer is exposed to this plasma for thedesired time, which may range from about 1 second to about 120 seconds.Oxygen plasma surface oxidation is performed in order to render thefront surface of the single crystal semiconductor donor substratehydrophilic and amenable to bonding to a single crystal semiconductorhandle substrate prepared according to the method described above.

The hydrophilic front surface of the single crystal semiconductor donorsubstrate 500 and the front surface of single crystal semiconductorhandle substrate 100 are next brought into intimate contact to therebyform a bonded structure. According to the methods of the presentinvention, each of the front surface of the single crystal semiconductordonor substrate 500 and the front surface of single crystalsemiconductor handle substrate 100 may comprise one or more insulatinglayers. The insulating layers form the dielectric layer of the bondedstructure. With reference to FIG. 2, an exemplary dielectric layer 420is shown. As depicted therein, the dielectric layer 420 of the bondedstructure may comprise a first oxide layer 200, a nitride layer 300, asecond oxide layer 400. Further configurations are within the scope ofthis disclosure.

Since the mechanical bond may be relatively weak, the bonded structuremay be further annealed to solidify the bond between the single crystalsemiconductor donor substrate 400 and the single crystal semiconductorhandle substrate 100 comprising the epitaxial layer 200 and thepolycrystalline silicon charge trapping layer 300. In some embodimentsof the present invention, the bonded structure is annealed at atemperature sufficient to form a thermally activated cleave plane in thesingle crystal semiconductor donor substrate. An example of a suitabletool might be a simple Box furnace, such as a Blue M model. In someembodiments, the bonded structure is annealed at a temperature of fromabout 200° C. to about 400° C., from about 300° C. to about 400° C.,such as from about 350° C. to about 400° C.

In some embodiments, the anneal may occur at relatively high pressures,such as between about 0.5 MPa and about 200 MPa, such as between about0.5 MPa and about 100 MPa, such as between about 0.5 MPa and about 50MPa, or between about 0.5 MPa and about 10 MPa, or between about 0.5 MPaand about 5 MPa. In conventional bonding methods, the temperature islikely limited by the “autocleave”. This occurs when the pressure of theplatelets at the implant plane exceeds the external isostatic pressure.Accordingly, conventional anneal may be limited to bonding temperaturesbetween about 350° C. and about 400° C. because of autocleave. Afterimplantation and bond, the wafers are weakly held together. But the gapbetween the wafers is sufficient to prevent gas penetration or escape.Weak bonds can be strengthened by heat treatments, but the cavitiesformed during implant are filled with gas. While heating, the gas insidethe cavities pressurizes. It is estimated that the pressure may reach0.2-1 GPa (Cherkashin et al., J. Appl. Phys. 118, 245301 (2015)),depending on the dosage. When the pressure exceeds a critical value, thelayer delaminates. This is referred to as an autocleave or thermalcleave. It prevents higher temperature or longer time in the anneal.According to some embodiments of the present invention, bonding occursat elevated pressures, e.g., between about 0.5 MPa and about 200 MPa,such as between about 0.5 MPa and about 100 MPa, such as between about0.5 MPa and about 50 MPa, or between about 0.5 MPa and about 10 MPa, orbetween about 0.5 MPa and about 5 MPa, which thereby enables bonding atelevated temperatures. In some embodiments, the bonded structure isannealed at a temperature of from about 300° C. to about 700° C., fromabout 400° C. to about 600° C., such as between about 400° C. and about450° C., or even between about 450° C. and about 600° C., or betweenabout 350° C. and about 450° C. Increasing the thermal budget will havea positive effect on the bond strength. Thermal annealing may occur fora duration of from about 0.5 hours to about 10 hour, such as betweenabout 0.5 hours and about 3 hours, preferably a duration of about 2hours. Thermal annealing within these temperatures ranges is sufficientto form a thermally activated cleave plane. In conventional bondinganneals, the edge of both the handle wafer and donor wafer may becomefar apart due to the roll off. In this area, there is no layer transfer.It is called the terrace. Pressurized bonding is expected to reduce thisterrace, extending the SOI layer further out towards the edge. Themechanism is based on trapped pockets of air being compressed and“zippering” outwards. After the thermal anneal to activate the cleaveplane, the bonded structure may be cleaved.

After the thermal anneal, the bond between the single crystal singlecrystal semiconductor donor substrate 500 and the single crystalsemiconductor handle substrate 100 is strong enough to initiate layertransfer via cleaving the bonded structure at the cleave plane. Cleavingmay occur according to techniques known in the art. In some embodiments,the bonded structure may be placed in a conventional cleave stationaffixed to stationary suction cups on one side and affixed by additionalsuction cups on a hinged arm on the other side. A crack is initiatednear the suction cup attachment and the movable arm pivots about thehinge cleaving the wafer apart. Cleaving removes a portion of thesemiconductor donor wafer, thereby leaving a single crystalsemiconductor device layer 600, preferably a silicon device layer, onthe semiconductor-on-insulator composite structure. See FIG. 3.

After cleaving, the cleaved structure may be subjected to a hightemperature anneal in order to further strengthen the bond between thetransferred device layer 600 and the single crystal semiconductor handlesubstrate 100. An example of a suitable tool might be a verticalfurnace, such as an ASM A400. In some preferred embodiments, the bondedstructure is annealed at a temperature of from about 1000° C. to about1200° C., preferably at about 1000° C. Thermal annealing may occur for aduration of from about 0.5 hours to about 8 hours, preferably a durationof about 4 hours. Thermal annealing within these temperatures ranges issufficient to strengthen the bond between the transferred device layerand the single crystal semiconductor handle substrate.

After the cleave and high temperature anneal, the bonded structure maybe subjected to a cleaning process designed to remove thin thermal oxideand clean particulates from the surface. In some embodiments, the singlecrystal semiconductor device layer may be brought to the desiredthickness and smoothness by subjecting to a vapor phase HCl etch processin a horizontal flow single wafer epitaxial reactor using H₂ as acarrier gas. In some embodiments, the semiconductor device layer 600 mayhave a thickness between about 20 nanometers and about 3 micrometers,such as between about 20 nanometers and about 2 micrometers, such asbetween about 20 nanometers and about 1.5 micrometers or between about1.5 micrometers and about 3 micrometers.

In some embodiments, an epitaxial layer may be deposited on thetransferred single crystal semiconductor device layer 600. A depositedepitaxial layer may comprise substantially the same electricalcharacteristics as the underlying single crystal semiconductor devicelayer 600. Alternatively, the epitaxial layer may comprise differentelectrical characteristics as the underlying single crystalsemiconductor device layer 600. An epitaxial layer may comprise amaterial selected from the group consisting of silicon, silicon carbide,silicon germanium, gallium arsenide, gallium nitride, indium phosphide,indium gallium arsenide, germanium, and combinations thereof. Dependingupon the desired properties of the final integrated circuit device, theepitaxial layer may comprise electrically active dopants, such as boron(p type), gallium (p type), aluminum (p type), indium (p type),phosphorus (n type), antimony (n type), and arsenic (n type). Theresistivity of the epitaxial layer may range from 1 to 50 Ohm-cm,typically, from 5 to 25 Ohm-cm. In some embodiments, the epitaxial layermay have a thickness between about 20 nanometers and about 3micrometers, such as between about 20 nanometers and about 2micrometers, such as between about 20 nanometers and about 1.5micrometers or between about 1.5 micrometers and about 3 micrometers.

The finished SOI wafer comprises the single crystal semiconductor handlesubstrate 100, the dielectric layer 420, and the semiconductor devicelayer 600, may then be subjected to end of line metrology inspectionsand cleaned a final time using typical SC1-SC2 process.

Having described the invention in detail, it will be apparent thatmodifications and variations are possible without departing from thescope of the invention defined in the appended claims.

When introducing elements of the present invention or the preferredembodiments(s) thereof, the articles “a”, “an”, “the” and “said” areintended to mean that there are one or more of the elements. The terms“comprising”, “including” and “having” are intended to be inclusive andmean that there may be additional elements other than the listedelements.

In view of the above, it will be seen that the several objects of theinvention are achieved and other advantageous results attained.

As various changes could be made in the above products and methodswithout departing from the scope of the invention, it is intended thatall matter contained in the above description and shown in theaccompanying drawings shall be interpreted as illustrative and not in alimiting sense.

1. A method of preparing a multilayer structure, the method comprising:bonding a donor dielectric layer on a front surface of a single crystalsilicon donor substrate to a front surface of a single crystal siliconhandle substrate to thereby form a bonded structure, wherein (i) thesingle crystal silicon semiconductor handle substrate comprises twomajor, generally parallel surfaces, one of which is the front surface ofthe single crystal silicon handle substrate and the other of which is aback surface of the single crystal silicon handle substrate, acircumferential edge joining the front surface and the back surface ofthe single crystal silicon handle substrate, a central plane between thefront surface and the back surface of the single crystal silicon handlesubstrate, and a bulk region between the front and back surfaces of thesingle crystal silicon handle substrate and (ii) the single crystalsilicon donor substrate comprises two major, generally parallelsurfaces, one of which is the front surface of the silicon donorsubstrate and the other of which is a back surface of the silicon donorsubstrate, a circumferential edge joining the front and back surfaces ofthe silicon donor substrate, a central plane between the front and backsurfaces of the silicon donor substrate, and a bulk region between thefront and back surfaces of the silicon donor substrate, and furtherwherein the single crystal silicon donor substrate comprises a cleaveplane; and annealing the bonded structure at a temperature and for aduration sufficient to strengthen the bond between the donor dielectriclayer of the single crystal silicon donor substrate and the frontsurface of the single crystal silicon handle substrate, whereinannealing occurs at a temperature between about 300° C. and about 700°C., and at a pressure between about 0.5 MPa and about 200 MPa. 2.(canceled)
 3. The method of claim 1 wherein the single crystal siliconhandle substrate comprises a single crystal silicon wafer sliced from asingle crystal silicon ingot grown by the Czochralski method or thefloat zone method.
 4. (canceled)
 5. The method of claim 1 wherein thesingle crystal silicon donor substrate comprises a single crystalsilicon wafer sliced from a single crystal silicon ingot grown by theCzochralski method or the float zone method.
 6. The method of claim 1wherein annealing occurs at a temperature from about 400° C. to about600° C., such as between about 400° C. and about 450° C., or evenbetween about 450° C. and about 600° C., or between about 350° C. andabout 450° C.
 7. The method of claim 1 wherein annealing occurs at apressure between about 0.5 MPa and about 100 MPa, such as between about0.5 MPa and about 50 MPa, or between about 0.5 MPa and about 10 MPa, orbetween about 0.5 MPa and about 5 MPa.
 8. The method of claim 1 whereinthe donor dielectric layer comprises a material selected from the groupconsisting of silicon dioxide, silicon oxynitride, silicon nitride,hafnium oxide, titanium oxide, zirconium oxide, lanthanum oxide, bariumoxide, and any combination thereof.
 9. The method of claim 1 wherein thedonor dielectric layer comprises a material selected from the groupconsisting of silicon dioxide, silicon oxynitride, silicon nitride, andany combination thereof.
 10. (canceled)
 11. The method of claim 1wherein the donor dielectric layer comprises a multilayer, eachinsulating layer within the multilayer comprising a material selectedfrom the group consisting of silicon dioxide, silicon oxynitride, andsilicon nitride.
 12. The method of claim 1 wherein the donor dielectriclayer comprises three layers, wherein the three layers comprise asilicon dioxide layer in interfacial contact with the front surface ofthe single crystal silicon donor substrate, a silicon nitride layer ininterfacial contact with the silicon dioxide layer, and a silicondioxide layer in interfacial contact with the silicon nitride layer. 13.The method of claim 1 wherein the donor dielectric layer comprises aninsulating layer having a thickness of at least about 10 nanometerthick, such as between about 10 nanometers and about 10,000 nanometers,between about 10 nanometers and about 5,000 nanometers, between 50nanometers and about 400 nanometers, or between about 100 nanometers andabout 400 nanometers, such as about 50 nanometers, 100 nanometers, or200 nanometers.
 14. The method of claim 1 wherein further comprisingmechanically cleaving the bonded structure at the cleave plane of thesingle crystal silicon donor substrate to thereby prepare a cleavedstructure comprising the single crystal silicon handle substrate, thedonor dielectric layer, and a single crystal silicon device layer.
 15. Amethod of preparing a multilayer structure, the method comprising:bonding a donor dielectric layer on a front surface of a single crystalsilicon donor substrate to a handle dielectric layer on a front surfaceof a single crystal silicon handle substrate to thereby form a bondedstructure, wherein (i) the single crystal silicon handle substratecomprises two major, generally parallel surfaces, one of which is thefront surface of the single crystal silicon handle substrate and theother of which is a back surface of the single crystal silicon handlesubstrate, a circumferential edge joining the front surface and the backsurface of the single crystal silicon handle substrate, a central planebetween the front surface and the back surface of the single crystalsilicon handle substrate, and a bulk region between the front and backsurfaces of the single crystal silicon handle substrate and (ii) thesingle crystal silicon donor substrate comprises two major, generallyparallel surfaces, one of which is the front surface of the silicondonor substrate and the other of which is a back surface of the silicondonor substrate, a circumferential edge joining the front and backsurfaces of the silicon donor substrate, a central plane between thefront and back surfaces of the silicon donor substrate, and a bulkregion between the front and back surfaces of the silicon donorsubstrate, and further wherein the single crystal silicon donorsubstrate comprises a cleave plane; and annealing the bonded structureat a temperature and for a duration sufficient to strengthen the bondbetween the donor dielectric layer of the single crystal silicon donorsubstrate and the front surface of the single crystal silicon handlesubstrate, wherein annealing occurs at a temperature between about 300°C. and about 700° C., and at a pressure between about 0.5 MPa and about200 MPa.
 16. (canceled)
 17. The method of claim 15 wherein the singlecrystal silicon handle substrate comprises a single crystal siliconwafer sliced from a single crystal silicon ingot grown by theCzochralski method or the float zone method.
 18. (canceled)
 19. Themethod of claim 15 wherein the single crystal silicon donor substratecomprises a single crystal silicon wafer sliced from a single crystalsilicon ingot grown by the Czochralski method or the float zone method.20. The method of claim 15 wherein the handle dielectric layer comprisesa doped oxide.
 21. The method of claim 15 wherein the handle dielectriclayer comprises a silicate glass selected from the group consisting ofphosphosilicate glass, borosilicate glass, borophosphosilicate glass,and any combination thereof.
 22. The method of claim 15 wherein thehandle dielectric layer comprises a flowable oxide.
 23. The method ofclaim 15 wherein the handle dielectric layer comprises a flowablesilazane.
 24. The method of claim 15 wherein handle dielectric layercomprises a flowable silsesquioxane.
 25. The method of claim 15 whereinannealing occurs at a temperature from about 400° C. to about 600° C.,such as between about 400° C. and about 450° C., or even between about450° C. and about 600° C., or between about 350° C. and about 450° C.26. The method of claim 15 wherein annealing occurs at a pressurebetween about 0.5 MPa and about 100 MPa, such as between about 0.5 MPaand about 50 MPa, or between about 0.5 MPa and about 10 MPa, or betweenabout 0.5 MPa and about 5 MPa.
 27. The method of claim 15 wherein thedonor dielectric layer comprises a material selected from the groupconsisting of silicon dioxide, silicon oxynitride, silicon nitride,hafnium oxide, titanium oxide, zirconium oxide, lanthanum oxide, bariumoxide, and any combination thereof.
 28. The method of claim 15 whereinthe donor dielectric layer comprises a material selected from the groupconsisting of silicon dioxide, silicon oxynitride, silicon nitride, andany combination thereof.
 29. (canceled)
 30. The method of claim 15wherein the donor dielectric layer comprises a multilayer, eachinsulating layer within the multilayer comprising a material selectedfrom the group consisting of silicon dioxide, silicon oxynitride, andsilicon nitride.
 31. The method of claim 15 wherein the donor dielectriclayer comprises three layers, wherein the three layers comprise asilicon dioxide layer in interfacial contact with the front surface ofthe single crystal silicon donor substrate, a silicon nitride layer ininterfacial contact with the silicon dioxide layer, and a silicondioxide layer in interfacial contact with the silicon nitride layer. 32.The method of claim 15 wherein the donor dielectric layer comprises aninsulating layer having a thickness of at least about 10 nanometerthick, such as between about 10 nanometers and about 10,000 nanometers,between about 10 nanometers and about 5,000 nanometers, between 50nanometers and about 400 nanometers, or between about 100 nanometers andabout 400 nanometers, such as about 50 nanometers, 100 nanometers, or200 nanometers.
 33. The method of claim 15 further comprisingmechanically cleaving the bonded structure at the cleave plane of thesingle crystal silicon donor substrate to thereby prepare a cleavedstructure comprising the single crystal silicon handle substrate, thehandle dielectric layer, the donor dielectric layer, and a singlecrystal silicon device layer.